(1) Field of the Invention
This invention relates to a novel method for oxidizing unsaturated aromatic compounds.
There are many oxidized products useful for an intermediate material for various agricultural chemicals, pharmaceuticals and the like which are obtained by oxidizing unsaturated aromatic compounds.
For example, an arylacetone such as 4-hydroxy-3-methoxyphenylacetone, 3, 4-dimethoxyphenylacetone, 3, 4-dihydroxyphenylacetone or the like is a compound used as an intermediate for manufacturing L-.alpha.-methyldopa which is employed as an antihypertensive agent. Furthermore, 2-(4-isobutylphenyl) propionaldehyde is utilized as an intermediate for 2-(4-isobutylphenyl) propionic acid (trade name: ibuprofen) having antiphologistic, antipyretic and lenitive actions, and (4-isobutylphenyl)acetaldehyde is an intermediate of (4-isobutylphenyl) acetic acid (trade name: ibufenac) having the same pharmacological effects as those of the former compound.
(2) Description of the Prior Art
Among these useful compounds, arylacetones exhibiting high utility and for which various manufacturing methods have heretofore been proposed will be described hereinbelow as a specific example thereof. There have been proposed the following typical methods as ones for manufacturing arylacetones.
(1) British Patent No. 1,119,612 discloses a method in which a peroxide such as peracetic acid or the like is allowed to act on 1-(3, 4-dimethoxyphenyl)propylene, and the resulting diol type product is treated with an acid material such as zinc chloride to obtain 3, 4-dimethoxyphenylacetone.
(2) French Patent No. 1,450,200 discloses a method in which 3, 4-dimethoxybenzaldehyde is reacted with .alpha.-chloropropionic acid ester in the presence of a strong alkali, and the reaction product is then treated with a strong acid to obtain 3, 4-dimethoxyphenylacetone.
(3) Journal of American Chemical Society (JACS), 77, 700 (1955) describes a method in which 3, 4-dimethoxyphenylacetonitrile is reacted with sodium ethoxide in a solvent such as ethyl acetate thereby to transform the former into an acetyl-member, and then the acetyl-member thus obtained is hydrolyzed to obtain 3, 4-dimethoxyphenylacetone.
The above described method 1) involves such problems in that an yield is low in the process of the treatment by the use of an acid material and that since a peroxide used is explosive, special care is required for handling the same.
Furthermore, in the method 2), it is difficult to state that the raw materials 3, 4-dimethoxybenzaldehyde and .alpha.-chloropropionic acid ester are easily available.
The method (3) involves such problems in that it is necessary to carry out the reaction in a system from which water has been strictly removed in case of using sodium ethoxide therein for the sake of preventing hydrolysis of such sodium ethoxide, that a yield is low in the hydrolysis step, and that the number of steps in the method becomes excessive as a whole if steps required for manufacturing a raw material 3, 4-dimethoxyphenylacetonitrile itself from an easily available chemical material are taken into consideration.
As discussed above, it must be said that all the manufacturing methods (1), (2) and (3) have not yet been satisfactory from industrial point of view.